PAVs will not benefit SFS. An SFS server (1 entity) can't be setup to do
multiple I/Os to the same minidisk. Therefore, the VM I/O dispatcher
doesn't have anything (ie. multiple I/Os) to spread out over the real
system attached Aliases.
Regards, Steve.
Steve Wilkins
IBM z/VM Development
Marcy Cortes
<[EMAIL PROTECTED]
ellsfargo.com> To
Sent by: The IBM IBMVM@LISTSERV.UARK.EDU
z/VM Operating cc
System
<[EMAIL PROTECTED] Subject
ARK.EDU> Re: PAV and SFS
06/21/2007 12:10
AM
Please respond to
The IBM z/VM
Operating System
<[EMAIL PROTECTED]
ARK.EDU>
It depends!
I think you have to study your perf data and decide where your i/o
contention is. We don't have it like we used to (pre IBM DS8000 and FICON
) --- have moved on to just CPU and memory issues :)
We've moved most of our disks to mod 9 (all of prod Linux and about 1/2 the
traditional CMS users) and the last 3 TB that went in I had them do mod 27
(makes creating large linux filesystems easier). Not using PAV anywhere.
We just don't see the i/o queue that would warrant the effort.
On the dev/test system with 100 linux virtual servers and not enough memory
(24G real), we have about 50 mod 3's for paging. I don't suspect moving
that to 16 mod 9's would be that much different. 16 is still pretty spread
out. Now, if I had 3 page vols, I woudn't dream of putting them on 1 mod 9
:)
It is a bit confusing for the perf guys though ---- since disk size does
not
show up in the perf data!!!
And, I understood SFS to work like Kris said. We have both 3s and 9s in
our
SFS - we always give it the whole vol (minus cyl 0 of course ).
Marcy Cortes
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-----Original Message-----
From: The IBM z/VM Operating System [mailto:[EMAIL PROTECTED] On
Behalf Of O'Brien, Dennis L
Sent: Wednesday, June 20, 2007 6:32 PM
To: IBMVM@LISTSERV.UARK.EDU
Subject: [IBMVM] PAV and SFS
Our DASD people have asked if they can replace our 3390-3 size DASD volumes
with 3390-9's. My tentative answer is that most of the volumes that
contain
minidisks can be moved, if the new DASD has PAV. CP areas such as paging
should remain on 3390-3. Our SFS servers have 3338-cylinder minidisks, one
per volume. My initial thought is that I could put 3 of them on a 3390-9
with two PAV aliases, and the SFS server could do one I/O to each minidisk
at the same time, just like it can when the minidisks are on separate
volumes.
In the recent "dasd 3390 -27" thread, Kris Buelens said, "For SFS though
(and probably DB2) PAV is maybe of limited help: a given SFS server will
start only one I/O to all its minidisks on the same disk." Is that really
true? Does an SFS server look at the real devices or volsers that its
minidisks are on, and only start an I/O to one minidisk on a volume at a
time?
Dennis O'Brien
The three R's of Windows problem resolution: Retry, Reboot, Reinstall.
